Corrosion Potential Behavior of Machined and Electrochemcially Oxidized Implants

Surgical procedures and implant aging may adversely affect corrosion behavior. Objectives: To determine the effects of scratching and material aging on the corrosion potential of machined and electrochemically oxidized titanium implants, as an indication of changes to the passivating oxide. Methods: Titanium Noble Biocare™ machined implants (Ma) (n=11) and electrochemically oxidized implants (TiUnite™) (Eo) (n=52) were studied in a human convenience sample (n=45). Corrosion potentials (vs. Ag/AgCl electrode) were measured on two occasions at each surgical stage: first stage surgery - Implant Placed, Screw Inserted; second stage surgery (>3 mo later) – Implant/Screw First Exposed, Screw Removed. The data were statistically analyzed using a mixed-effects model. Results: The much more positive Implant Placed mean corrosion potential of Eo implants [-30 (87) mV] vs. Ma implants [-313 (61) mV] (p<0.001) at first-stage surgery was probably due mainly to the electrochemically thickened oxide on Eo implants. Screw Inserted [Ma: -412 (81) mV; Eo: –229 (98) mV] and Screw Removed [Ma: -496 (155) mV; Eo: –398 (91) mV] showed a significantly decreased mean corrosion potential for both implant types (p<0.01), indicating oxide abrasion. At second-stage surgery, the Implant/Screw First Exposed mean corrosion potential of Ma implants [-285 (83) mV] was not significantly different from the Implant Placed mean [-313 (61) mV] (p=0.40), consistent with repassivation, whereas the Implant/Screw First Exposed mean corrosion potential of Eo implants [-230 (93) mV] was substantially less than the Implant Placed mean [–30 (87) mV] (p<0.001). Since titanium is expected to repassivate, it is suggested that this mean corrosion potential drop of Eo implants was due to oxide thinning during the healing period. Conclusions: Drops in mean corrosion potential following Screw Inserted and Screw Removed indicated surgical procedures temporarily increased corrosion. Additionally, the oxidizing power of the bioenvironment was unable to maintain the thickened oxide of Eo implants.